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U.S. Chemical Warfare Service drills at Presidio Barracks, San Francisco, California

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Men in the trenches with gas masks on ready to go over the top. Photographer: Charles Feinberg. National Archives and Records Administration, cataloged under the National Archives Identifier (NAID) 26423782. (This image is a work of a U.S. military or Department of Defense employee, taken or made as part of that person's official duties. As a work of the U.S. federal government, the image is in the public domain in the United States. Photograph edited by Dr. Douglas J Lanska.)